Christmas Trees
Ed Peachey and Chal Landgren
Revised November 20, 2008

Excessive weed growth in Christmas trees reduces tree vigor, increases vertebrate pests, and can reduce the quality of the product if plant debris is lodged among branches. However, completely eliminating all vegetation increases runoff, soil erosion, and soil compaction and can diminish quality if branches get muddy during harvest. Consequently, vegetation management in Christmas trees requires weed control practices combined with careful management of the ground cover to maintain tree growth, quality, and ease of harvest while reducing soil erosion and compaction.
Weed shifts   Weed infestations are dynamic and change depending on new species introductions and previous cultural and weed control practices. For example, routine cultivation, mowing, or use of the same or similar herbicides will result in a weed shift to species that tolerate these practices. Examples include prostrate weeds that tolerate flailing, deep-rooted or easily spread perennials that tolerate cultivation, and weeds such as common groundsel, field bindweed, and false dandelion that resist repeated applications of the same or similar herbicides.
Preventing weed shifts   Weeds that survive cultivation, mowing or flailing, specific herbicide treatments, or other routine cultural practices must be eliminated before the tolerant species or biotypes become established. Combine a variety of weed control practices or treatments; rotate fields, cultural practices, and herbicides; and spot treat with a hoe or registered herbicide when the weed first appears. Also, clean equipment when moving from an infested field.
Ground covers   Some growers manage vegetation such as subclover, grass or weedy vegetation between rows for 1 to 2 yr before harvest to reduce soil erosion, improve traffic conditions in wet weather, and reduce mud on harvested trees. New grass varieties—including dwarf cultivars such as  'Aurora Gold' and 'Soil Guard', which respond to minimal management practices such as drought, low fertility or sublethal rates of postemergence herbicides—are being introduced into various horticultural cropping systems. Consult your local Extension agent or get recent information about living mulches and their management.
Managing weedy vegetation   Successful vegetation management in Christmas trees requires a comprehensive or year-round approach whereby a combination of weed control practices is used and alternated over several years. Developing these strategies requires knowledge of each weed and weed control practice. Identify weeds and gather information about the effectiveness of each weed control practice. Consider costs and select herbicide combinations that can be applied together or in split applications that control the weeds in the crop without damage to trees. Note the action of each herbicide (how the chemical works in the plant), then tank-mix and alternate use of these products to reduce the chance of developing resistant species or biotypes. Often a combination of mechanical or herbicidal treatments, and sometimes hand removal or spot treatment with herbicide sprays or wipers, will provide the most effective year-round control.
Soil-active herbicides   Persistent, soil-applied herbicides can be applied to weed-free soil during winter when rain will activate the chemical. Apply lower rates on sandy soils with lower clay, organic matter, or cation exchange capacities. Existing vegetation can be controlled by mixing a postemergence contact or translocated herbicide. Consult labels for listed conifer species.
Postemergence herbicides   These are applied to weeds once they emerge, often at a specific weed growth stage either as a directed spay away from the tree or over the trees in specific situations. For example, clopyralid (e.g., Stinger) may control selected thistles if applied at the proper weed growth stage and may be sprayed over the top of selected tree species. Glyphosate (e.g., Roundup) is typically applied as a directed spray and controls many weeds but must be applied at the correct stage of weed growth to obtain maximum movement of the product into the roots (see label for details). Avoid applications to green bark, low limbs, or crop foliage. Two postemergence grass herbicides (Poast and Fusilade)  can be applied to actively growing grasses in the four- to five-leaf stage for optimum results. More mature grasses can be controlled but often require two applications. Annual bluegrass and all fine fescues resist these products.
Note   Herbicides must be applied at the correct rate and time to selectively control weed growth with minimal chance of injury to trees. Obtain more consistent results by reading the herbicide label and other information about the proper application and timing of each herbicide. Good record keeping regarding plant growth stages, rates, surfactants, and weather will also help. Suggested rates listed in this guide are stated as pounds active ingredient per acre (lb ai/A) or pounds acid equivalent per acre (lb ae/A). For band applications under tree rows, reduce quantity of herbicide applied proportionately to the area within the row actually sprayed.
Some products are not recommended for first-year seedlings and/or some stock-types, such as container seedlings, that may be more susceptible to damage using soil-active herbicides due to the light-textured potting mix.

CHRISTMAS TREES—Site Preparation 
•  glyphosate (numerous product names)
Rate  Consult labels
Time  Apply lower rates to actively growing annual weeds.
Remarks  Consult label for higher rates and time of application for perennial weeds. Inhibits production of three amino acids and protein synthesis
Caution  Do not exceed 10.6 lb ai/A per year
Site of action  Group 9: inhibits EPSP synthase
Chemical family  None generally accepted
CHRISTMAS TREES—New Plantings
•  hexazinone (Velpar DF)
Rate  1 to 1.5 lb ai/A (1.33 to 2 lb/A Velpar DF, depending on soil texture)
Time  Registered for new plantings. However, variable tree injury has been observed. Therefore, before using this product on new plantings, treat small areas to become familiar with the results and conditions of applications.
Remarks  Consult label for specific rates and precautions on newly planted trees. Later applications in early April may be more effective than March applications due to greater leaching from spring rains. Higher rates are effective on trailing blackberries
Caution Restricted-use herbicide in Washington. 
Site of action  Group 5: photosystem II inhibitor
Chemical family  Triazinone
•  atrazine  (several products)
Rate  2 to 4 lb ai/A (4 to 8 pints/A Atrazine 4L)
Time  To ensure activation, apply in March or April after soil settles from transplanting but before rains stop.
Remarks  Atrazine can be applied either pre- or postemergence. Avoid applying over actively growing trees unless applied immediately before or during a rain. Do not exceed 4 lb ai/A per year.
Caution  A restricted-use herbicide.  
Site of action  Group 5: photosystem II inhibitor
Chemical family  Triazinone
•  isoxaben (Gallery 75 DF or Gallery T&V)
Rate  0.495 to 0.998 lb ai/A (0.66 to 1.33 lb/A)
Time  Apply to debris-free soil surface in late summer to early fall, in early spring, or immediately after cultivating.
Remarks  Identify weeds and adjust rates according to charts on label. Activate with 0.5 inch water or shallow cultivation before weeds begin to emerge. Chemical stability remains adequate when left on soil surface for 21 days.
Caution  Do not apply to newly transplanted crops until soil settles.
Site of action  Group 21: inhibits cell wall synthesis Site B
Chemical family  Benzamide
•  isoxaben + trifluralin (Snapshot 2.5TG) 
Rate  200 lb/A
Time  Apply to weed- and debris-free soil. Soil must be settled with water and free of cracks after transplanting.
Remarks  Activate within 3 days using 0.5 inch of water or shallow cultivation before weeds begin to emerge. Follow label instructions for repeat treatments.
Site of action  (isoxaben) Group 21: inhibits cell wall synthesis Site B; (trifluralin) Group 3: microtubule assembly inhibitor
Chemical family  (isoxaben) benzamide; (trifluralin) dinitroaniline
•  oryzalin (Surflan A.S.)
Rate  2 to 4 lb ai/A (2 to 4 quarts/A)
Time  Apply in pine and fir (but not Douglas-fir) Christmas tree plantations to bare soil surface after transplanting and settling.
Remarks  Activate with 0.5 inch water or shallow cultivation before weeds emerge.
Site of action  Group 3: microtubule assembly inhibitor
Chemical family  Dinitroaniline
•  prodiamine (Barricade 4FL and Barricade 65 WG)
Rate  0.65 to 1.5 lb ai/A (21 to 48 fl oz/A Barricade 4FL)
Time  Apply to weed-free site in fall or spring before weed seeds have germinated; follow with 0.5-inch rain or irrigation or shallow incorporation within 14 days.
Remarks  Inhibits mitosis in roots and shoots. Application may injure trees with new and actively growing shoots; delay application until shoots harden off, or apply immediately before a rain so that product is washed from leaves.
Caution  Do not exceed maximum rate listed on label in a 12-mo period.
Site of action  Group 3: microtubule assembly inhibitor
Chemical family  Dinitroaniline
•  pendimethalin (Pendulum 3.3EC)
Rate  2 to 4 lb ai/A (2.4 to 4.8 quarts/A depending on length of control desired)
Time  Apply at planting or before weed seeds germinate. 
Remarks  Soil should be loose and free of all established weeds. Water within a few days to activate herbicide before weeds emerge. Inhibits mitosis in roots and shoots.
Site of action  Group 3: microtubule assembly inhibitor
Chemical family  Dinitroaniline
•  fluazifop (Fusilade DX)
Rate  0.25 to 0.375 lb ai/A (16 to 24 fl oz/A)
Time  Apply to actively growing grasses in early spring, following ample rain, as a directed spray with 0.25% nonionic surfactant.
Remarks  Identify grasses and adjust rates depending on susceptibility and stage of weed growth according to label instructions. Results often are erratic on grasses stressed from lack of vigor, drought, high temperature, or low fertility. More mature grasses and quackgrass can be controlled but may require two applications. Annual bluegrass and all fine fescues resist treatment. Inhibits fatty acid production, cell membranes, and new growth.
Caution  Do not tank-mix with other pesticides or apply within 5 days of other pesticide treatments. Grazing is prohibited. 
Site of action  Group 1: acetyl CoA carboxylase (ACCase) inhibitor
Chemical family  Aryloxyphenoxy propionate
•  sethoxydim (Segment )
Rate  0.28 to 0.47 lb ai/A (36 to 60 fl oz/A)
Time  Apply at optimum growth stage listed on the label.
Remarks  Identify susceptible grasses. Control often is erratic on grasses stunted or stressed from drought, high temperatures, or low fertility. Resistant grasses include annual bluegrass and all fine fescues, whereas quackgrass can be suppressed. Inhibits fatty acid production, cell membranes, and new growth.
Site of action  Group 1: acetyl CoA carboxylase (ACCase) inhibitor
Chemical family  Cyclohexanedione
•  oxyfluorfen (Goal 2XL or Galigan 2E)
Rate  1 to 2 lb ai/A
Time  Apply immediately after transplanting but before budbreak, over tree tops or as directed spray. 
Remarks  Controls small emerged broadleaf weeds with brief soil residual. Perennial emerged annual grasses are not controlled, although fine fescues may be suppressed. Acts as contact, either directly on broadleaf weeds or at soil surface as weeds emerge.
Site of action  Group 14: inhibits protoporphyrinogen oxidase
Chemical family  Diphenylether
CHRISTMAS TREES—Established Plantings—Winter Applications that Persist in Soil
•  hexazinone (Velpar L)
Rate  1 to 2 lb ai/A
Time  Apply in spring before conifer bud break.
Remarks  Requires some moisture to activate in soil but less than required for atrazine. Consult label for specific doses and precautions depending on type of soil and soil organic matter content. If trees are growing actively, apply as a directed spray to reduce chance of injury. Later applications in early April may be more effective than March applications due to greater leaching from spring rains.
Caution. Restricted use herbicide in Washington
Site of action  Group 5: photosystem II inhibitor
Chemical family  Triazinone
•  atrazine  (several products)
Rate  2 to 4 lb ai/A (4 to 8 pints/A Atrazine 4L)
Time  Apply February through March to dormant trees. Apply atrazine before annual weeds are 1.5 inches tall; use higher rates for quackgrass control.
Remarks  Avoid applying over actively growing trees unless applied immediately before or during a rain. Do not exceed 4 lb ai/A per year.
Caution  A restricted-use herbicide.  
Site of action  Group 5: photosystem II inhibitor
Chemical family  Triazinone
•  simazine (several products)
Rate  2 to 4 lb ai/A
Time  Fall or spring.
Remarks  Simazine must be applied before weeds emerge. One application per year unless to control quackgrass. Avoid applying over actively growing trees unless applied immediately before or during a rain.
Caution  A restricted-use herbicide.  Wait to apply simazine for at least 1 yr after transplanting. In Idaho, do not apply simazine to trees less than 3 yr old. 
Site of action  Group 5: photosystem II inhibitor
Chemical family  Triazine
•  hexazinone + sulfometuron (Westar DG)
Rate  1 to 1.5 lb/A Westar DG, depending on soil texture and tree species; consult label
Time  Apply either before or soon after weeds emerge, when weeds are small and actively growing. Apply broadcast only to dormant trees. If trees have broken dormancy, directed applications are required to avoid contact with new growth.
Remarks  Recommended for Douglas-fir, Fraser fir, grand fir, noble fir, Nordman fir, and Turkish fir. For other species, apply first to small areas to determine selectivity.
Caution  Surfactants are not recommended and may cause excessive injury. For maximum safety to grand fir, use large transplant stock and apply at 1 to 1.25 lb/A, or use after trees have been established at least one growing season. In newly transplanted fields, rain or irrigation should have settled soil. Hexazinone is a restricted-use herbicide in Washington.
Site of action  (hexazinone) Group 5: photosystem II inhibitor; (sulfometuron) Group 2: acetolactate synthase (ALS) inhibitor
Chemical family  (hexazinone) triazinone; (sulfometuron) sulfonylurea
•  isoxaben (Gallery 75DF or Gallery T&V)
Rate  0.495 to 0.998 lb ai/A (0.66 to 1.33 lb/A)
Time  Apply to debris-free soil surface in late summer to early fall, in early spring, or immediately after cultivation.
Remarks  Identify weeds and adjust rates according to charts on label. Activate with 0.5 inch water or shallow cultivation before weeds begin to emerge. Chemical stability remains adequate when left on soil surface for 21 days.
Caution  Do not apply to newly transplanted crops until soil settles.
Site of action  Group 21: inhibits cell wall biosynthesis Site B
Chemical family  Benzamide
•  isoxaben + trifluralin (Snapshot 2.5TG) 
Rate  200 lb/A
Time  Apply to weed- and debris-free soil.
Remarks  Activate within 3 days using 0.5 inch of water or shallow cultivation before weeds begin to emerge. Follow label instructions for repeat treatments.
Site of action  (isoxaben) Group 21: inhibits cell wall biosynthesis Site B; (trifluralin) Group 3: microtubule assembly inhibitor
Chemical family  (isoxaben) benzamide; (trifluralin) dinitroaniline
•  prodiamine (Barricade FL)
Rate  0.65 to 1.5 lb ai/A (21 to 48 oz/A Barricade 4FL)
Time  Apply to weed-free site; follow with 0.5-inch rain or irrigation or shallow incorporation.
Caution  Do not exceed maximum rate listed on label in a 12-mo period.
Site of action  Group 3: microtubule assembly inhibitor
Chemical family  Dinitroaniline
•  pendimethalin (Pendulum 3.3EC or 2G)
Rate  2 to 4 lb ai/A (2.4 to 4.8 quarts/A depending on length of control desired)
Time  Apply before weed seeds germinate. Tank-mix with glyphosate, glufosinate, or labeled burndown herbicides to control existing vegetation.
Remarks  Soil should be loose and free of all established weeds. Water within a few days to activate herbicide before weeds emerge. Inhibits mitosis in roots and shoots.
Site of action  Group 3: microtubule assembly inhibitor
Chemical family  Dinitroaniline
•  pronamide (Kerb 50W)
Rate  1 to 2 lb ai/A (2 to 4 lb/A)
Time  Make a single application in fall, before freezing weather.
Remarks  Not recommended on trees less than 1 yr old. Use higher rates for quackgrass and finer soils. Requires soil moisture to activate. Primarily for grass control. Degraded by microorganisms in warmer weather. Special local needs labels OR-040029 and WA-060002 for aerial application of Kerb 50W. Inhibits cell division or mitosis.
Caution  A restricted-use pesticide. Preharvest interval is 1 yr.
Site of action  Group 3: microtubule assembly inhibitor
Chemical family  Benzamide
•  dichlobenil (Casoron CS)
Rate  1.96 to 3.92 lb ai/A (1.4 to 4.3 gal/A)
Time  Apply midwinter immediately before a cold rain, to reduce volatility and enhance weed suppression.
Remarks  Liquid formulation of encapsulated crystals of dichlobenil. Controls most germinating seeds and seedlings of annual and perennial grasses and broadleaf weeds. 
Caution  Use only around well-established plants; typically wait until 1 yr after transplanting. Do not use on light sandy soils. Do not apply with high or gusty wind, high temperatures, low humidity, or temperature inversions. Grazing livestock is prohibited. Inhibits cellulose and cell wall formation. 
Site of action  Group 20: inhibits cell wall synthesis Site A
Chemical family  Nitrile
•  oryzalin (Surflan) +
•  simazine (Princep 4L)
Rate  2 to 4 lb ai/A of each product
Time  Apply to weed-free soil after transplant or in spring when 0.5 to 2 inches of rain will activate herbicide.
Remarks  Surflan label has tank-mix with Princep.
Caution  Wait at least 1 yr after transplanting to apply simazine in Oregon and Washington. Do not apply to trees less than 2 yr old in Idaho. Princep is not labeled for use on grand or noble fir.
Site of action  (oryzalin) Group 3: microtubule assembly inhibitor; (simazine) Group 5: photosystem II inhibitor
Chemical family  (oryzalin) dinitroaniline; (simazine) triazine
•  oryzalin + benefin (XL 2G)
except Douglas-fir and eastern hemlock
Rate  200 lb/A (2 to 4 mo of weed control) to 400 lb/A (4 to 8 mo of weed control)
Time  Apply to established Christmas trees before target weed species emerge. Established plantings are those that have been transplanted to their final location, and soil has settled with rain or irrigation.
Remarks  Controls winter or summer annual grasses and broadleaves. At least 0.5 inch of rain or irrigation is required to activate herbicides. If rain does not fall in 21 days, cultivate to activate. Does not control emerged species. For maximum efficacy, soil should be free of weeds and clod size small. Do not exceed 800 lb/A per season; allow 2 mo between applications.
Caution  Not for Douglas-fir or eastern hemlock.
Site of action  (both) Group 3: microtubule assembly inhibitor
Chemical family  (both) dinitroaniline
•  oxyfluorfen (Goal 2XL, Galigan H2O, Galigan 2E, Goal Tender)
Rate  1 to 2 lb ai/A (4 to 8 pints/A Goal 2XL; 2 to 4 pints/A Goal Tender)
Time  Apply over trees or as directed spray throughout the year, except when buds and new shoot growth are tender and not yet hardened off.
Remarks  Controls small emerged broadleaf weeds with brief soil residual. Perennial and emerged annual grasses are not controlled, although fine fescues may be suppressed. Acts as contact, either directly on broadleaf weeds or at soil surface as weeds emerge.
Caution  Do not apply in combination with glyphosate or other products with oil or surfactant additives until adequately tested. 
Site of action  Group 14: inhibits protoporphyrinogen oxidase
Chemical family  Diphenylether
•  flufenacet + metribuzin (Axiom DF)
Douglas-fir and true firs only
Rate  12 to 20 oz/A
Time  Apply pre- or very early postemergence to weeds when trees are completely dormant. Trees must be established at least one growing season.
Remarks  Special local needs labels OR-040017 and WA-030023.
Caution  Metribuzin is a restricted-use pesticide in Washington. Do not apply more than once per production year or within 11 mo of last treatment.
Site of action  (flufenacet) Group 15: inhibits very long chain fatty acid synthesis; (metribuzin) Group 5: photosystem II inhibitor
Chemical family  (flufenacet) oxyacetamide; (metribuzin) triazinone
CHRISTMAS TREES—Established Plantings—Broadcast or Directed Applications 
•  atrazine + 2,4-D isooctyl ester (Shotgun) 
Rate  3 to 4 pints/A for broadleaf weeds to 4 inches; 5 to 6 pints/A for longer control and for grasses (6 pints = 1.7 lb ai/A atrazine and 0.75 lb ae/A 2,4-D).
Time  Apply February through March to dormant trees, before budbreak, or in the fall if rain is more consistent then. Apply before annual weeds are 1.5 inches tall. Use higher rates for quackgrass control. 
Remarks  For established conifers of all types. Used as a directed spray between and around trees. 
Caution  Atrazine is a restricted-use herbicide. In Idaho, do not apply to trees less than 3 yr old. 
Site of action  (atrazine) Group 5: photosystem II inhibitor; (2,4-D) Group 4: synthetic auxin
Chemical family  (atrazine) triazine; (2,4-D) phenoxy acetic acid
•  asulam (Asulox)
Rate  3.34 lb ai/A (1 gal/A)
Time  For bracken fern control. Apply after Christmas tree terminal buds mature and bracken fronds are fully expanded.
Remarks  Lower than labeled rate usually is effective and is advised. Inhibits cell division or mitosis.
Caution  Do not graze treated areas.
Site of action  Group 18: inhibits DHP synthase step
Chemical family  Carbamate
•  fluazifop (Fusilade DX)
Rate  0.25 to 0.375 lb ai/A (16 to 24 fl oz/A)
Time  Apply to actively growing grasses in early spring following ample rain. Check label for recommended maximum growth stages of weeds. Apply as a directed spray with 1% crop oil concentrate or 0.25% nonionic surfactant.
Remarks  Identify grasses and adjust rates depending on susceptibility and stage of weed growth as label instructs. Results often are erratic on grasses stressed from lack of vigor, drought, high temperature, or low fertility. More mature grasses and quackgrass can be controlled but may require two applications. Annual bluegrass and all fine fescues resist treatment. Inhibits fatty acid production, cell membranes, and new growth.
Caution  Do not tank-mix with other pesticides or apply within 5 days of other pesticide treatments. Grazing is prohibited. 
Site of action  Group 1: acetyl CoA carboxylase (ACCase) inhibitor
Chemical family  Aryloxyphenoxy propionate
•  sethoxydim (Segment)
Rate  0.28 to 0.47 lb ai/A (36 to 60 fl oz/A)
Time  Apply at optimum growth stage listed on the label.
Remarks  Identify susceptible grasses. Control often is erratic on grasses stunted or stressed from drought, high temperatures, or low fertility. Resistant grasses include annual bluegrass and all fine fescues; quackgrass can be suppressed.  Inhibits fatty acid production, cell membranes, and new growth.
Caution  Do not mix or apply with any other pesticide, additive, or fertilizer except as specified on the label. 
Site of action  Group 1: acetyl CoA carboxylase (ACCase) inhibitor
Chemical family  Cyclohexanedione
•  clethodim (Envoy and others)
Douglas-fir, grand fir, and pines
Rate  0.095 to  0.25 lb ai/A (13 to 34 fl oz/A depending on grass species)
Time  Apply postemergence to actively growing annual or perennial grasses as listed on label.
Remarks  Consider environmental and plant growth conditions that affect leaf uptake; see label for guidelines.
Caution  Do not exceed 68 fl oz/A per season.
Site of action  Group 1: acetyl CoA carboxylase (ACCase) inhibitor
Chemical family  Cyclohexanedione
•  clopyralid (Stinger)
Rate  0.09 to 0.25 lb ae/A (0.25 to 0.67 pint/A)
Time  Apply broadcast or in bands during active weed growth up to five-leaf stage.
Remarks  Note fir, pine, and spruce along with rates to control annual weeds, Canada thistle, and knapweeds listed on label. To avoid needle curling, do not apply during first year after transplanting. Mimics natural plant hormones.
Caution  Do not exceed 0.67 pint/A per season or 0.5 pint/A for blue spruce. Do not use on Scots pine. Do not add surfactant or crop oil. 
Site of action  Group 4: synthetic auxin
Chemical family  Pyridine
•  2,4-D LV4
Rate  0.48 to 0.95 lb ae/A (1 to 2 pints/A)
Time  Apply over-the-top as a broadcast treatment when trees are dormant using a low rate, or direct spot sprays toward actively growing weeds before budbreak or after budset during cool weather.
Remarks  Read label carefully. Mimics natural plant hormones. May be tank-mixed with atrazine. 
Caution  Do not apply over the tops of pine or true firs (Abies spp.)
Site of action  Group 4: synthetic auxin
Chemical family  Phenoxy acetic acid
•  glyphosate (numerous product names)
Rate  Spray—consult labels
Time  Select application equipment to prevent crop injury by directing spray toward base of plants or with selective applicators.
Remarks  Adjust concentration depending on equipment, or consult label about rate and time of application, especially for perennial weeds. Additional surfactant or mixing ammonium sulfate as label instructs may improve control of slightly stressed weeds. Avoid contact of spray or mist with foliage or green bark of desirable plants. Inhibits production of three amino acids and protein.
Caution  Do not exceed 10.6 lb ai/A per year. Repeated glyphosate applications created resistant biotypes of ryegrass in Australian orchards. To avoid weed resistance, rotate herbicides and weed control practices. 
Site of action  Group 9: inhibits EPSP synthase
Chemical family  None generally accepted
•  glyphosate (several products)
Rate  Wiper—33% solution
Time  Consult label for best time to apply to specific weeds.
Remarks  Avoid contact with desirable vegetation. In severe infestations, reduce equipment ground speed or apply in two directions to ensure contact with wiper.
Site of action  Group 9: inhibits EPSP synthase
Chemical family  None generally accepted
•  glufosinate (Finale)
Rate  Directed application—2 to 6 quarts/A; spot treatment—2 to 4 fl oz/1 gal of water
Time  Apply to actively growing weeds.
Remarks  Do not let spray or drift contact living tissue or green, thin, or uncalloused bark, as injury may occur.
Caution  Do not broadcast over Christmas trees.
Site of action  Group 10: inhibits glutamine synthetase
Chemical family  Phosphinic acid
•  clopyralid (Stinger)
Rate  0.09 to 0.19 lb ae/A (0.25 to 0.5 pint/A for broadleaves; 0.5 to 0.66 pint/A for difficult-to-control perennials)
Time  Apply broadcast over tree tops when broadleaf weeds are growing actively, from emergence to five-leaf stage. For perennials such as Canada thistle, apply after most basal leaves have emerged and before bud stage. 
Remarks  Can be applied over the tops of trees in Pacific Northwest. Use with caution on 1-yr-old trees; new leaves in first-year trees may curl. Avoid using surfactants or crop oils.
Site of action  Group 4: synthetic auxin
Chemical family  Pyridine
•  triclopyr (Garlon 3A)
Rate  0.75 to 1.875 lb ae/A (2 to 5 pints/A)
Time  Apply in late summer or early fall after trees’ terminal growth has hardened off but before target weeds drop leaves.
Remarks  To control woody plants and perennial and broadleaf weeds. Select application equipment to prevent tree injury by directing spray toward base of plants or with selective applicators.
Caution  Garlon spray solution can injure needles and branches.
Site of action  Group 4: synthetic auxin
Chemical family  Carboxylic acid

Herbicide Effectiveness on Weeds in Christmas Trees
	Cultural	Soil-applied Herbicides	Postemergence	
	Cultivation	Mowing	atrazine	simazine	hexazinone (Velpar)	Hexazinone + sulfometuron	pronamide (Kerb)	oryzalin (Surflan)	0ryzalin + benefin	glyphosate	oxyfluorfen (Goal)	asulam (Asulox)	fluazifop (Fusilade)	sethoxydim (Poast)	triclopyr (Garlon 3)	
Broadleaf Weeds
Bindweed, field	
R	
R	
R	
R	
—	—	
R	
R	R	
M	
S+	
—	
R	
R	
M	
Clovers	M*	R	R	R	S	S	R	R	R	M	S	R	R	R	S	
Dandelion	R	R+	R	R	S	S	R	R	R	S	S*	R	R	R	S	
Dandelion, false	R	R	R	R	S	S	R	R	R	S	S*	M	R	R	S	
Dock, curly	M*	R	R	R	M	M	S*	R	R	—	S*	M	R	R	—	
Filaree	M*	R	—	—	S	S	R	—	S	M	S	—	R	R	S	
Hawksbeard	S*	M+	—	—	—	—	R	—	-	M	S	—	R	R	—	
Knotweed	M*	R	S	M*	S	S	M	M*	S	R	M	—	R	R	—	
Lambsquarters	S*	S	S	S	S	S	M	S*	S	S	S	—	R	R	—	
Lettuce, prickly	S*	S	S	S	S	S	R	R	M	M	S	—	R	R	—	
Mustards	S*	S	S	S	S	S	M	R	M	S	M	—	R	R	—	
Pigweed	S*	S	S	S	S	S	M	S*	S	S	S	—	R	R	—	
Plantain	S*	R	S*	S*	—	—	R	R	R	S	S*	R	R	R	—	
Queen Anne’s lace	S*	M+	—	—	—	—	R	R	R	—	—	—	R	R	—	
Ragwort, tansy	M*	R	—	—	—	—	R	R	R	R	—	M	R	R		
Sowthistle, annual	S*	S	S	S	S	S	R	R	M	S	S	—	R	R	—	
Sowthistle, perennial	R	R+	—	—	—	—	R	R	R	S	R	R	R	R	—	
Thistle, bull	M*	M	S*	S*	—	—	R	M*	M	S	S*	R	R	R	S	
Thistle, Canada	R	R+	M*	R	—	—	R	R	R	S	S+	R	R	R	S	
Vetch	M*	M+	M*	M*	—	—	R	R	R	M	M	—	R	R	S	
Grass Weeds
Barnyardgrass	
S*	
R	
S*	
S*	
S	
S	
M	
S*	
S	
S	
R	
—	
S	
S	
R	
Bentgrass	R	R+	S	—	—	—	S	R	R	S	—	—	S	S	R	
Bluegrass, annual	S*	R	S	S	S	S	S	S*	S	S	S*	S	R	R	R	
Bromegrasses	S*	R	S	S	S	S	S	S*	S	S	S*	—	S	M	R	
Fescues, fine	—	—	—	—	—	M	—	—	—-	M	—	—	R	R	R	
Fescues, tall	S*	R+	R	R	M	S	S	M	M*	S	S*	R	S	S	R	
Orchardgrass	R	R+	R	R	M	M	S	R	R	M	—	M	S	S	R	
Quackgrass	R	R+	M	R	S	S	S	R	R	M	—	R	M	R	R	
Ryegrass, annual	S*	R	S*	S*	S	S	S	S	S*	S	S*	R	M	S	R	
Ryegrass, perennial	R	R+	R	R	M	M	S	R	R	S	—	M	M	S	R	
Velvetgrass	R	R+	R	R	S	S	S	R	R	S	—	—	M	S-M	R	
Woody Species
Alder	
R	
R+	
R	
R	
R	
R	
R	
R	
R	
M	
R	
R	
R	
R	
S	
Blackberry,  
   evergreen	
R	
R+	
R	
R	
S	
R	
R	
R	
R	
M	
R	
R	
R	
R	
S	
   Himalaya	R	R+	R	R	S	R	R	R	R	S	R	R	R	R	S	
   trailing	R	R+	R	R	M	M	R	R	R	S	R	R	R	R	S	
Cherry 	R	R+	R	R	R	R	R	R	R	S	R	R	R	R	R	
Cottonwood	R	R+	R	R	—	—	R	R	R	M	R	R	R	R	S	
Maple	R	R+	R	R	R	R	R	R	R	M	R	R	R	R	M	
Maple, vine	R	R+	R	R	R	R	R	R	R	M	R	R	R	R	S	
Oak	R	R+	R	R	R	R	R	R	R	S	R	R	R	R	M	
Poison-oak	R	R+	R	R	R	R	R	R	R	M	R	R	R	R	S	
Salal	R	R+	R	R	R	R	R	R	R	R	R	R	R	R	R	
Willow	R	R+	R	R	R	R	R	R	R	M	R	R	R	R	M	
Other Weeds
Fern, bracken	
R+	
R+	
R	
R	
M	
M	
R	
R	
R	
S	
R	
S	
R	
R	
R	
Horsetail, field	R+	R+	R	R	—	—	R	R	R	R	R	M	R	R	R	
S = susceptible to herbicide or easily controlled with cultivation or mowing
M = moderate control or suppression of weed competition can be expected under normal conditions 
R = weeds resist treatments or competition is not significantly reduced
 * = seedlings controlled only; biennial or perennial stages resistant             + = vegetative control only